#include <stdio.h>

double Harmonic_Mean(double i, double j);

int main(void)
{
    double mean, i, j;
    scanf("%lf %lf", &i, &j);  
    mean = Harmonic_Mean(i, j);
    printf("%f\r\n", mean);
    
    return 0;
}

double Harmonic_Mean(double i, double j)
{
    double mean;
    mean = 1 /(1 / i + 1 / j) / 2;

    return mean;
}